Just in case three aren't enough to go around, there's one more Jonas brother.

At 7 years old, Frankie — a.k.a. "Bonus Jonas" — is camera-ready. He made his MTV debut this week on "TRL," along with his famous brothers. And by blood association alone, this kid knows a thing or two about mugging for the camera.

"Actually, I don't really know [how I got the nickname]," he said on "TRL," his older brothers by his side. "It just came up, and people started talking to me and going, 'Hey, Bonus Jonas,' and I was like, 'Hey, whatever.' "

On the show, Bonus Jonas also had the lofty task of picking fans to come up to the studio, and his brothers admit that he's perhaps the hardest Jonas brother to impress.

"He'll tell it straight up, and he'll be mean if he needs to," Kevin said, with Joe adding, "He's a good critic. He's a mini Simon Cowell."

The boys love Frankie so much that even his off-color jokes about Nick's diabetes amuse them to no end. At a press conference last week, Nick said, "Once I got comfortable with [having diabetes], Frankie used to call me 'Pancreas Boy,' but he's the cutest kid alive so he can get away with it."

Despite the jokes, Frankie's brothers say he's also been very mature when it comes to dealing with the disease. "I remember sitting down with [Frankie] and said, 'Nick is in the hospital, and he'll be home in a couple of days,' " Kevin recalled. "He hugged us and he said, 'He'll be OK.' "

But don't think this one "TRL" appearance is the last time you'll see Frankie. He wants to follow in his older brothers' footsteps and go into show business. There are unconfirmed Internet reports that he will be joining his brothers when they get their own sitcom.

On top of that, Bonus Jonas also has his own musical endeavor in the works. It's a project that his brothers fully support. "He's always telling us that his band he's making ... he's always saying, 'You guys are going to open for me,' " Joe teased on "TRL." "He's a funny little guy."